Tuesday, 12 July 2016

How bad is bottled water, really?

I have been asked to look at the relative carbon emissions from tap water versus bottled water. Many people seem to think that our mains water supply is a significant source of greenhouse gas emissions. It is not, at least in the volumes we use for drinking. However bottled water certainly is - partly due to the bottle and partly due to the distance it is transported. The greenhouse gas emissions for bottled water are 200 - 600 times as much as tap water.

Here are some summary figures.

WatergCO2e/litre
Tap water
0.5
Bottled water best case: from local source in 1.5 litre bottles, 50% recycled plastic
118
Bottled water worse case: from a distant source such as San Pellegrino, in 0.5 litre bottles, virgin plastic
322

For comparison, a typical UK resident will generate about 30kg CO2/day so one litre of bottled water per day could be 1% of this.


All greenhouse gas emissions in this post are per litre of water.

Tap water
Water supply (including extraction, purification and pumping) 0.5g CO2e/litre

Water supply involves extracting the water, filtering it, purifying it and then pumping it through the mains pipes. This varies from one region to another. Extraction from an aquifer may involve pumping but aquifer water is generally very clean and needs little treatment. The energy for distribution depends mainly on the height you have to lift the water so will be much greater in hilly areas than in flat ones. (Water sources are invariably down in a valley, not on a hill).

Cambridge water company is now part of the South Staffordshire Water group. South Staffs gets their water mainly from rivers and has a lot of hills while Cambridge gets its water from aquifers and is mainly flat. Based on 2013/2014 data, South Staffordshire carbon emissions were 0.46 gCO2/litre supplied while in Cambridge they were less than half that at 0.2 gCO2/litre supplied.

These figure do not include the other side of the water process - collecting and handling sewerage. That is typically as much again or a little more.

The average figure of 0.5 g/litre is a little out of date (2008) and may be on the high side.

Data sources:
Average water supply emissions from Future Water (www.gov.uk) 2008.
GHG emissions for South Staffordshire and Cambridge are from Cambridge Water Company.

Unfortunately, since 2014 water companies do not have to report greenhouse gas emissions as one of their Key Performance Indicators. They only have to report the savings.

Bottled mineral water

Mineral water sources are quite similar to mains water sources. They typically come from an aquifer or a spring. They need to be filtered and possibly sterilised before bottling. The GHG emissions at this stage are probably less than tap water emissions. The main emissions are from bottling and transport.

The bottles

gCO2e/litre0.5l bottles (x2)1.5l bottles (x2/3)
Virgin PET
134
92
50% recycled
93
64


Tap water is delivered through pipes which can be made of a variety of materials, commonly plastic. However, those pipes have a long lifetime and the GHG emissions per litre transported is negligible.

Most plastic bottles are made from PET which is one of those plastics where there are big savings to be made from recycling. Also, the industry has put a lot of effort into making the bottles thinner and with less plastic in them - 30% less or more. They seem more 'crinkly' these days and not very strong. They are designed for one use only so they do not need to be.

Bigger bottles have proportionately less plastic for the volume of water, so these are environmentally more sustainable.

Glass bottles have higher carbon emissions both for manufacture (even using recycled glass) and for transport because they are heavier.

Data sources:
Mass of bottles from British Plastics Federation.
The emissions due to the bottles (PET/kg) from PlanetSave: A message about your water bottle.


Transportation

San Pellegrino to London (1300 km): 188g
Evian to London (1000km): 134g

Malvern to London (187km): 25g

Mains water comes to us through pipes, possibly from only a few miles away. There will always be some pumps involved to maintain pressure but mainly the pumps are needed to lift the water from valley to hilltop. There is much less energy needed than to deliver bottled water in lorries.

The figures shown assume that transport is in a medium sized articulated lorry (less than 33 tonnes). Transport in smaller, rigid lorries would generate 3 times these emissions or more.

Data sources:
Carbon factors from transport are from the government conversion factors for company reporting. Assumes an articulated lorry.

Transportation from supermarket to home

In a car, 5km (3 miles) round trip with 18 litres: 44g

Bottled water is heavy. Maybe you could cycle to and from the supermarket except that the water would be too heavy so you take the car instead. This calculation is based on a carrying a tray of 12 x 1.5 litre bottles so 18 litres total in a medium sized car.

Data sources:
Carbon factors for the car are from the government conversion factors for company reporting. Assumes a lower medium diesel car.

What if I don't like the tap water?
Tap water is perfectly healthy to drink. The levels of chlorine that you may find will not cause you harm. However, if you find you can taste the chlorine, put some water in a jug in the fridge for 12 hours and see if that is OK for you. If you can still taste it, try a jug filter. These are quite inexpensive to buy, though you will have to replace the filters regularly.

If you are likely to want water while you are travelling, take tap water with you. You can use one of those bottles designed for camping or sports that can be washed in the dishwasher. Some of them are little thermos flasks that can keep the water cold.

If you really want mineral water on a regular basis, buy it in big bottles and choose one that does not have far to travel. You can treat yourself to more exotic water on special occasions.


1 comment:

  1. Other problems are these packaged or bottled water is stored for longer periods and at higher temperatures compare to pipe distribution systems. RS Glass Bottle

    ReplyDelete